This invention relates to a lifting jack for automobiles and other vehicles. More particularly, it relates to an improvement in the construction of a pantograph jack to reduce the length of the drive screw and the space required for storage.
A portable jack is often stored in a vehicle to enable a driver to lift the vehicle to effect emergency repairs, for example, to change a tire. One popular type of jack for automobiles is the pantograph jack. Known pantograph jacks typically have four arms hinged in a parallelogram at four joints. One joint is located on a base of the jack. Another joint is positioned at a load rest vertically above the base. Two other free floating joints are located on a horizontal diagonal at opposite comers of the parallelogram formed by the arms. When the free floating joints are drawn together in a horizontal plane the arms extend vertically to lift the load support with respect to the base and vice versa. The relative position of the free floating joints is controlled by a drive screw or threaded shaft which links them together.
Modem automobile design places increasing emphasis on efficient use of space. In turn, jack manufacturers have focused attention on reducing the amount of trunk space required for jack storage. It is has been found that it is often more space efficient to store a pantograph jack in a diamond or square shape rather than in either of the fully extended or lowered positions. A problem is encountered in this configuration, however. The drive screw must be long enough to span between the free floating joints in the fully lowered position. Therefore, in the partially lowered diamond shape, the drive screw extends outside the parallelogram of the arms. Extra storage space is then required to accommodate the projecting portion of the screw.
The present invention is directed to an improvement in the construction of a pantograph jack to reduce or eliminate the projection of the drive screw in the partially lowered jack position.
The invention is an extension mechanism attached to one of the free floating joints, hereafter the first joint, which projects a threaded annulus along the diagonal towards the second free floating joint thereby reducing the length required of the drive screw.
More particularly, the improvement of this invention relates to a pantograph jack having a base to position the jack on a ground support, a load rest to fit under and to carry a vehicle, a parallelogram pantograph and a drive screw. The pantograph has first and second arms hinged at the base, third and fourth arms hinged at the load rest, first and third arms hinged at a first joint and second and fourth arms hinged at a second joint, with the first and second joints on an approximately horizontal diagonal of the pantograph. The drive screw is mounted between the first and second joints to rotate about an axis coextensive with the diagonal. The length of the drive screw is sufficient to connect between the first and second joints when the jack is in a fully lowered position. The jack has a trunnion nut moans pivotally mounted in the first joint which has a threaded annulus to engage the drive screw. Rotation of the drive screw within the threaded annulus drives the first joint linearly along the drive screw. There is also a trunnion bearing means pivotally mounted in the second joint having an opening to receive an unthreaded portion of the drive screw in a rotatable but linearly fixed connection relative to the drive screw.
The improvement of this invention comprises a trunnion nut means having an extension means to extend the threaded annulus along the diagonal towards the second joint and a drive screw having a length sufficient to span from the trunnion bearing means of the second joint into the threaded annulus of the trunnion nut means of the first joint when the jack is in the fully lowered position.